The invention relates to cutting tools and, in particular, to cutting inserts and toolholders therefor that effect location of the insert at a selected position on the toolholder with improved accuracy and reliability, and a method of locating such inserts. More particularly, the invention provides inserts and toolholders wherein the inserts are located in the toolholder using reference surface or surfaces close to the active cutting edge and substantially independent of contact between the flanks of the insert and the toolholder.
In the cutting tool industry, it is a conventional practice to use cutting toolholders, e.g. mills, drills, lathes, reamers, bores, cutters, blades and other known cutting devices, having replaceable cutting inserts of hard wear resistant material releasably secured thereto. The toolholders are manufactured with recesses or pockets therein, to hold and support the cutting insert, either alone or coupled with an insert-holding cartridge. Generally, the insert has multiple cutting edges or cutting edge portions and only one or two of them are put in contact with the workpiece at any one time. The cutting edge or edges positioned in the toolholder to contact the workpiece are referred to as active cutting edges. In this manner, when the active cutting edges of the insert become dull or the insert otherwise fails, the less expensive insert is indexed to an unused cutting edge which becomes xe2x80x9cactivexe2x80x9d or replaced rather than replacing or repairing an entire tool.
The use of inserts has provided cost savings in materials and labor, as well as allowing use of materials for the cutting insert that are different from the toolholder material. However, the use of replaceable inserts has also created challenges in positioning the insert uniformly, accurately and repeatably in the toolholder in a selected orientation, that is, to locate the insert. Another challenge presented by insert use is to limit movement of the insert relative to the toolholder during use. Location is critical to overall tool performance including the tolerances that can be maintained, reliability of the tool, down time and tool life. Historically, cutting edges integral with a cutting tool, such as the teeth on a hand saw, had a fixed position relative to the tool body and movement of the cutting edge was limited by characteristics of the tool material. The use of inserts as individual parts of a cutting tool, separate from the toolholder, introduced new variables that contribute to inaccuracy in positioning of the active cutting edge. Variables that affect position of the active cutting edge in the toolholder include, but are not limited to, variations in size or shape from insert to insert, variations in the distance between features on the same insert, variations in geometrical forms on the insert, variations in toolholder pocket sidewalls and position of the pocket. Use of inserts also increased the potential for movement of the insert (and hence the cutting edge) relative to the toolholder during use.
Locating an insert involves positioning the insert at a selected location on the toolholder, relative to the x, y and z axes of three-dimensional space, and during use the insert""s movement on these axes, translationally and rotationally, relative to the toolholder should approach zero. Additionally, in order to maintain accuracy of a cutting process when a used cutting edge is changed for an unused edge, it is desirable that the user be able to position the insert in the toolholder such that the unused cutting edge is located in nearly the identical place in relation to the toolholder and workpiece as was the former cutting edge. This challenge is multiplied when a tool holds more than one insert since the inserts"" positions in the pockets relative to each other also affect cutting. Various known holding means, such as screws and clamps, are used in the industry to secure cutting inserts in toolholders. Heretofore, holding means have been used in conjunction with the sidewalls of the pockets in the toolholder to locate the insert.
Conventionally, an insert positioned in a toolholder has bottom and flank (side) surfaces in contact with the pocket walls, and has at least one cutting edge that is formed by intersection of the top surface with the flanks. A portion of the cutting edge extends beyond the toolholder for contacting the workpiece. The sidewalls of the toolholder pockets are routinely utilized as locating surfaces for the insert. Users push inserts into toolholder pockets until the insert flanks proximate to the pocket sidewalls abut the sidewalls along at least a portion of the flank length. The insert is then releasably secured, with the flanks abutting toolholder pocket sidewalls, by a holding means. In this conventional locating method, the insert flanks determine the position of the insert, relative to the toolholder, by contact between the insert flanks proximate to the pocket sidewalls and the pocket sidewalls, and thereby dictate the position of the active cutting edges on the portion of the insert extending beyond the toolholder. The pocket sidewalls also support the insert and are designed to prevent it from moving out of the selected position due to forces generated by contact with the workpiece. That is, in the prior art, the flanks of the insert and the pocket sidewalls are used to locate the insert. A disadvantage of prior art locating means has been inaccurate location of the active cutting edge of the insert in relation to the workpiece. U.S. Pat. No. 3,813,746 to Price recognized problems that prior art cutting tools have with insert location, noting that as a practical matter, cutting edges will not always be located at exactly the same position in relation to the holder. Price discloses a locking pin used to wedge an insert flank against a toolholder pocket sidewall and seeks to limit variation in cutting edge position by inclining the pocket sidewall to reduce forward and rearward insert displacement. Heretofore other attempts have been made to reduce or eliminate positioning variables, including the following:
U.S. Pat. No. 3,911,543 to Sorice discloses an elongated cutting insert with a locating pin. The insert engages the rear, side and bottom wall of the toolholder pocket.
U.S. Pat. No. 4,028,782 to Stansak discloses an insert having notches in upper and lower surfaces which correspond to the toolholder pocket. Precision indexing is accomplished by indexing surfaces positioned on the flanks of the insert.
U.S. Pat. No. 4,244,666 to Erickson et al. discloses a locking pin that tilts to locate the insert against the back wall of the toolholder pocket.
U.S. Pat. No. 4,420,280 to Gustafson discloses a toolholder with a locking pin on an insert holder engaging the central hole of an insert and a clamping wedge which moves the insert holder. The clamping wedge engages the insert holder thereby moving the locking pin and insert and locating the insert by abutment of the insert flank with a stop on the toolholder. Spring means push the insert away from the stop when the clamp is released.
U.S. Pat. No. 4,525,110 to Stojanovski discloses ball nose end mill inserts having recesses which are acted upon by protuberances on a cap to locate the insert against a toolholder pocket sidewall.
U.S. Pat. No. 5,035,544 to Ikenaga et al. U.S. Pat. No. 3,837,058 to Barkley et al., and U.S. Pat. No. 5,586,844 to Nyman disclose various examples of a toolholder with a locking pin which engages the central hole of an insert and a clamping wedge attached to the toolholder by a screw. A rear end of the clamping wedge assembly engages an inclined supporting surface and a front end of the clamping wedge assembly engages the insert flank. Location of the insert on the pin is made by the wedge with reference to the insert flank. U.S. Pat. No. 5,682,803 to Boianjiu discloses an insert or shim having a pattern of protrusions designed to indent the flat toolholder pocket when a clamp secures the insert to prevent movement during use. The insert may have a protrusion, which fits a recess in the shim.
The foregoing prior art attempts to secure inserts still have drawbacks associated with using insert flanks and toolholder pockets as reference surfaces for locating the active cutting edge, and provide inaccurate cutting edge location.
Another drawback in conventionally locating prior art inserts in toolholders has been inability to maintain the position of the cutting edge, and therefore the workpiece finish, to within desired tolerances in a given size insert. It is known in the industry that, as the distance between the locating surface and the active cutting edge increases, the difficulty of maintaining that distance to within a selected tolerance during insert manufacture increases. This phenomenon is recognized in manufacturing standards and grades of precision. For example, DIN standard 7160 DY5 qualifies articles of various dimensions as having met the xe2x80x9ch7xe2x80x9d grade of precision based upon the tolerances that the article holds. However, the margin for error gets larger as the size of the part increases. Comparing two articles that meet the xe2x80x9ch7xe2x80x9d grade, a 100 mm long article and a 10 mm long article, shows that the tolerances required are not the same. The larger article meets the xe2x80x9ch7xe2x80x9d grade provided it is within xc2x117.5 microns of the desired dimension. The smaller article must hold more stringent tolerances of xc2x17.5 microns to achieve the same xe2x80x9ch7xe2x80x9d grade of precision. This manufacturing standard, and others, recognize that it is more difficult to maintain a selected tolerance, of xe2x80x9cxc2x1xxe2x80x9d units of measurement, on a dimension as the size of the dimension increases. Due to this phenomenon, the greater the length dimension (distance) between the locating surface on the insert and the cutting edge being located (active cutting edge), the more difficult it is to maintain the location of the cutting edge to a selected tolerance. This is a major disadvantage of the prior art location means, which typically locate the insert using the insert flanks farthest away from the cutting edge being located. The distance between the active cutting edge and the flank of the insert distant from the cutting edge is dictated by the size of the insert, which is often not amenable to a different selection. Applicants"" invention reduces this inaccuracy by placing the insert locating units close to the cutting edge being located, and is independent of insert size.
During use of a cutting tool, movement of the cutting insert in relation to the toolholder introduces another source of inaccuracy. For example, xe2x80x9cinsert risexe2x80x9d is characterized by movement of the insert in relation to the pocket walls. This movement is caused by forces exerted on the insert when it contacts the workpiece. It is known in the industry that the forces exerted on an insert in a toolholder during cutting act to move the insert in one or more of six degrees of freedom of movement of the insert. The six degrees of freedom designate the six possible types of directional movement that can be imparted to an object, such as an insert, when a force is exerted thereon, and correspond to translational or rotational movement in relation to the conventional x, y, z axes that describe three dimensional space. In the prior art, attempts are made to limit the degrees of freedom of movement of the insert by locating the insert against the toolholder pocket floor and one or more sidewalls, and then securing the insert with a clamp or other holding means. However, inaccuracies in positioning the active cutting edge and in movement of the insert during use remain in conventional cutting tools.
Yet another disadvantage of the prior art has been the need for precision machining of the toolholder pockets. Since the floor and usually two sidewalls are used to locate the insert, all three of these surfaces must be precisely machined to avoid irregularities such as incorrect angular relationships, improper pocket size and surface irregularities all of which can change the position of the insert relative to the workpiece either during use or when the insert is exchanged for a new one. The precision required of the toolholder pockets results in increased costs for the design and manufacture of toolholders. Particularly where the pocket geometry is complex or difficult to machine, creating a pocket or series of pockets having sidewalls in precise relation to each other and the tool body is costly and time consuming. Even precision machined pockets do not achieve the tolerance requirements for some machining applications.
The foregoing drawbacks in conventional location devices have been recognized in he industry. Prior art attempts to use location means other than the pocket sidewall have resorted to adding parts external to the insert periphery which contact the insert flanks, thereby perpetuating inaccuracies attributable to variations in the insert. U.S. Pat. No. 4,632,606 to Lagerberg discloses a localization pin that contacts a hole in a cutting insert on two separate centering surfaces. The flanks of the insert abut support surfaces on a plate attached to the toolholder and slide along these surfaces until the localization pin is wedged in the insert hole, thereby locating with reference to the insert flanks. U.S. Pat. No. 4,714,384 to Lagerberg discloses a toolholder with a locking pin which engages a hole of an insert and a two part clamping assembly attached to the toolholder. The clamping assembly engages the insert flanks pushing the insert onto the pin. These designs continue to use the insert flanks as a reference and have the drawback of making the tool larger and heavier. Increased size in a cutting tool can interfere with certain cutting operations. Further, the heavier the tool becomes, the greater the forces that are exerted on the insert when the tool is in motion and the greater the dynamic inaccuracy of the location of the cutting edge. The prior art attempts often decrease accuracy due to numerous movable parts external to the periphery of the insert and may exhibit tool imbalances. Another disadvantage of several of the prior art location devices has been limited capability to withstand the extreme forces generated on the cutting tool. As machine tools achieve higher revolution per minute capabilities and speeds and feed rates are increased, heavy tools and those having numerous movable parts become more undesirable.
Applicants have developed a new cutting insert and toolholder geometry that provides excellent locating accuracy and simplicity of manufacture, and a method of locating a cutting insert in a toolholder employing the new geometries which overcome the foregoing disadvantages.
It is an object of the present invention to provide an insert, toolholder, cutting tool and method of locating an insert, which overcome the disadvantages of the prior art. It is, therefore, an object of this invention to provide an insert and toolholder design which provides excellent accuracy and reliability in locating the insert in a tool body or holder. A more particular object of the invention is to provide a method for uniformly, accurately and repeatably locating an insert in a tool body or holder in a selected orientation.
It is an object of the invention to provide a new method and features for locating the insert in the toolholder with greater uniformity, accuracy and repeatability, and limit the insert""s freedom of movement during use. A further object of the invention is to provide mating engagement of locating units having a bearing surface or surfaces extending through 360xc2x0.
It is an object of the invention to provide an improved cutting tool having an insert or inserts located in a toolholder substantially independent of contact between the toolholder pocket sidewalls and the insert flanks.
It is an object of the invention to provide an improved cutting tool with locating units, in particular moving parts thereof, internal to the toolholder body and insert body during use. It is a further object of the invention to provide an insert locating unit, in particular the locator elements and bearing surfaces thereof that are internal to the peripheral flanks and top surface of the insert being located.
It is another object of the invention to provide an insert that is located by one or more bearing surfaces during manufacture and located by the same bearing surface or surfaces in the use environment.
It is an object of the invention to increase the precision of locating inserts by reducing the distance between the locating surfaces, such as the bearing surface or surfaces, and the active cutting edge being located thereby improving tolerances which can be met. It is also an object of the invention to increase the precision of locating the active cutting edge of larger inserts by eliminating the effect of the increase in insert size on tolerances that can be met by locating without reference to the opposite flank.
Applicants"" invention also relates to a method of locating a cutting insert in a toolholder by positioning an insert having a first locating unit in aligned relation with a toolholder having a second locating unit adapted to mate with the first locating unit, the first locating unit comprising at least one stationary locator element and the second locating unit comprising at least one toolholder locator element, such that one of the stationary locator elements is matingly engagable with one of the toolholder locator elements, matingly engaging the first and second locating unit and exerting force on one of the locating unit whereby the insert""s location in the toolholder is determined by abutment of selected bearing surface or surfaces of the first and second locating unit, and substantially independent of insert flank position.
It is an object of the invention to provide a cutting tool having a toolholder with an insert receiving region having an insert receiving seat, and a cutting insert securable within the region having a first locating unit disposed on the insert body, the first locating unit comprising first and second stationary locator elements disposed on at least one of the surfaces, the first stationary locator element positioned proximate a cutting edge to be located, as well as a second locating unit disposed in the insert receiving region, the second locating unit comprising first and second toolholder locator elements, at least one of the toolholder locator elements being adapted to matingly engage at least one of the stationary locator elements, the locator elements comprising bearing surfaces. The tool also has a tensioning device for urging bearing surface on one of the toolholder locator elements into abutment with the bearing surface of the first stationary locator element.
It is another object of the invention to provide a tool having a toolholder having a toolholder body comprising an insert receiving region having an insert receiving seat, a toolholder locating unit disposed in the insert receiving seat; an insert having a body defined by a top surface, a bottom surface and at least one flank extending therebetween, and at least one cutting edge formed by intersection of one of the flanks and one of the surface or surfaces, the insert being releasably secured on the insert receiving seat, an insert locating unit disposed on one of the surface or surfaces and adapted to matingly engage the toolholder locating unit; and a tool periphery, that is an outline or profile of the tool, formed by combining outlines of the insert receiving region and the insert, the toolholder locating unit and the insert locating unit being encompassed by the tool periphery, whereby the locating units lie internal to the bodies.
It is a further object of the invention to provide a toolholder for holding a cutting insert, having a toolholder body and an insert receiving region comprising an insert receiving seat for contacting the bottom surface and a toolholder locating unit for matingly engaging the insert locating unit; the insert receiving seat having a distal portion for supporting the active cutting edge during use; the toolholder locating unit comprising a first toolholder locator element disposed on the distal portion and having reference bearing surface or surfaces for abutting first insert locator element bearing surface or surfaces proximate the active cutting edge; and a second toolholder locator element for engaging a second insert locator element and having second bearing surface or surfaces for contacting second insert locator element bearing surface or surfaces; one of the first and second toolholder locator elements being movable in relation to the toolholder body for urging the first insert locator element bearing surface or surfaces against the first toolholder locator element bearing surface or surfaces; and a tensioning device for moving one of the first and second toolholder locator elements.
It is another object of the invention to provide a toolholder for holding a cutting insert, comprising an insert receiving seat for contacting the bottom surface of an insert, the seat having a distal end for supporting an insert cutting edge during contact between the cutting edge and a workpiece, and a locating unit for locating the insert on the seat substantially independent of contact between the insert flanks and the toolholder, the locating unit comprising a toolholder stationary locator element for mating engagement with a stationary locator element positioned on the insert bottom surface, the toolholder stationary locator element positioned on the distal end, a movable locator element for bringing bearing surface or surfaces on the stationary locator elements into mutual abutment and a tensioning device for actuating the movable locator element.
It is also an object of the invention to provide a cutting insert of hard wear resistant material releasably securable in a toolholder comprising a top and bottom surface or surfaces, at least one flank extending therebetween, a cutting edge formed by intersection of the at least one flank and the top surface, at least a portion of the cutting edge being an active cutting edge during use, an insert locating unit for engaging a toolholder locating unit disposed on the toolholder, comprising a plurality of locator elements disposed on the surface or surfaces and internal to the at least one flank, at least one of the locator elements positioned proximate the active cutting edge and adapted to matingly engage a toolholder locator element positioned in an insert receiving region of a toolholder, bearing surface or surfaces on the locator elements for contacting adjacent bearing surface or surfaces on the toolholder locating unit during mating engagement in response to forces exerted by a tensioning device on the toolholder, thereby locating the active cutting edge substantially independent of contact between the at least one flank and the toolholder.
It is a yet further object of the invention to provide a cutting insert wherein the locator elements comprise bores for matingly engaging pins on a toolholder and bearing surface or surfaces circumscribing the bore for frictionally limiting rotational and translational movement of the insert.